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cgroup, memcg, cpuset: implement cgroup_taskset_for_each_leader()

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It wasn't explicitly documented but, when a process is being migrated,
cpuset and memcg depend on cgroup_taskset_first() returning the
threadgroup leader; however, this approach is somewhat ghetto and
would no longer work for the planned multi-process migration.

This patch introduces explicit cgroup_taskset_for_each_leader() which
iterates over only the threadgroup leaders and replaces
cgroup_taskset_first() usages for accessing the leader with it.

This prepares both memcg and cpuset for multi-process migration.  This
patch also updates the documentation for cgroup_taskset_for_each() to
clarify the iteration rules and removes comments mentioning task
ordering in tasksets.

v2: A previous patch which added threadgroup leader test was dropped.
    Patch updated accordingly.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
This commit is contained in:
Tejun Heo 2015-09-11 15:00:19 -04:00
parent 3df9ca0a2b
commit 4530eddb59
4 changed files with 41 additions and 18 deletions
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22
include/linux/cgroup.h
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@ -232,11 +232,33 @@ void css_task_iter_end(struct css_task_iter *it);
* cgroup_taskset_for_each - iterate cgroup_taskset
* @task: the loop cursor
* @tset: taskset to iterate
*
* @tset may contain multiple tasks and they may belong to multiple
* processes. When there are multiple tasks in @tset, if a task of a
* process is in @tset, all tasks of the process are in @tset. Also, all
* are guaranteed to share the same source and destination csses.
*
* Iteration is not in any specific order.
*/
#define cgroup_taskset_for_each(task, tset) \
for ((task) = cgroup_taskset_first((tset)); (task); \
(task) = cgroup_taskset_next((tset)))
/**
* cgroup_taskset_for_each_leader - iterate group leaders in a cgroup_taskset
* @leader: the loop cursor
* @tset: takset to iterate
*
* Iterate threadgroup leaders of @tset. For single-task migrations, @tset
* may not contain any.
*/
#define cgroup_taskset_for_each_leader(leader, tset) \
for ((leader) = cgroup_taskset_first((tset)); (leader); \
(leader) = cgroup_taskset_next((tset))) \
if ((leader) != (leader)->group_leader) \
; \
else
/*
* Inline functions.
*/